Barricades of molded plastic have been known for some time. They typically include two panel units hinged together so that they can be spread apart for use and folded and collapsed for storage or transport. The individual panel units are one piece, integral, hollow plastic panels, formed by rotational or blow molding. The hollow plastic panels may be filled with sand as ballast to make them withstand wind forces. Examples of plastic barricades of the type described above are illustrated in Glass U.S. Pat. Nos. 4,298,186 and 4,624,210.
Since the plastic barricades are by nature smooth and slippery and have substantially planar outside faces, if they are stacked together (for example, for storage) the stability of a number of stacked units is less than desired at times.